int main( int argc, char **argv )
{
  QCoreApplication app( argc, argv );

  QImage image( 300,200, QImage::Format_RGB32 );
  image.fill(0xFFFFFF);
  QPainter painter( &image );
  painter.drawText(100,100,"Hello, world!");
  
  image.save( "test.png", "PNG" );
  return 0;
}

#include <QApplication>
#include <QImage>
#include <QPainter>

#include <qwt_plot.h>
#include <qwt_plot_curve.h>
#include <qwt_plot_grid.h>
#include <qwt_legend.h>

static void output( QwtPlot *plot )
{
  const int width  = 600;
  const int height = 400;

  QImage image( width,height, QImage::Format_RGB32 );
  image.fill(0xFFFFFF);
  QPainter painter( &image );
  plot->print( &painter, QRect(10,10,width-20,height-20) );
  image.save( "test.png", "PNG" );
}

static void setData( QwtPlotCurve *curve )
{
  QVector<double> x,y;
  for(int i=0;i<1000;i++)
  { x << i;
    y << sin((double)i/1000*2*3.1415926);
  }
  curve->setData( x,y );
}

int main( int argc, char **argv )
{
  QApplication app( argc, argv, true );

  QwtPlot plot;

  QwtPlotGrid grid;
  grid.enableXMin(true);
  grid.enableYMin(true);
  grid.setMajPen(QPen(Qt::black, 1, Qt::DotLine));
  grid.setMinPen(QPen(Qt::gray, 1, Qt::DotLine));
  grid.attach( &plot );

  plot.setCanvasBackground(QColor("linen"));
  plot.setAxisScale(QwtPlot::yLeft,-1,1);
  plot.insertLegend(new QwtLegend, QwtPlot::BottomLegend);

  QwtPlotCurve curve;
  curve.setPen(QPen(Qt::darkBlue,2));
  curve.setTitle("sin");  
  setData( &curve );
  curve.attach( &plot );

  app.processEvents();

  output( &plot );

  return 0;
}

TEMPLATE = app
CONFIG  += console
SOURCES = test.cpp

win32{
INCLUDEPATH += $$[QT_INSTALL_PREFIX]/include/Qwt
LIBS        += -lqwt5 
}
unix{
INCLUDEPATH += /usr/local/qwt/include
LIBS        += -lqwt
}

QWidget: Cannot create a QWidget when no GUI is being used

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.